The present invention relates to full mesh optical interconnects including optical midplanes and backplanes for interconnecting electronic systems particularly communications systems. The optical interconnect provides dedicated high bandwidth connections between each circuit board assembly and every other circuit board assembly within a given electronics system.
Communication systems, especially those developed for scaleable high bandwidth systems, require interconnects more particularly referred to herein as backplanes in order to interconnect circuit board assemblies comprising the system. Backplanes are the ordinary means of providing such interconnection. In practice, ordinary electrical backplanes normally require a multitude of electrical connections for each circuit board in the system, thus reducing the reliability of the system. Additionally, each circuit board in the system must share the communications paths on electrical backplanes so that only a fraction of the overall bandwidth is available to each circuit board. Furthermore the sharing of resources is detrimental to system reliability in that a failure on one circuit board assembly is likely reduce the utility of the shared paths for all circuit boards. In communications systems where redundant subsystems are more commonly used, ordinary backplanes provide redundancy only at great expense. Finally, electrical backplanes are well known to be a source of electromagnetic emissions and crosstalk whereas an optical transmission guide emits no measurable radiation in the RF spectrum and there is no capacitive or magnetic coupling.
Other optical interconnection systems have been devised, however most are either costly systems that comprise a number of expensive optical elements like embedded fiber-optic cable and related connectors, mirrors, turning mirrors, holographic elements, graded index materials or lenses. The prior art also contains a few examples of inventions that attempt to provide the necessary function of perpendicular routings of signals from one circuit board assembly to the next but do so by utilizing unproven, undefined or costly manufacturing processes or require fundamental changes to the construction of the associated printed circuit board assemblies. In yet other inventions, optical interconnection methods rely on a line of sight connection, the bonding of fiber-optic cables to integrated circuit waveguides or connections on a single printed circuit board assembly. In the case of electrical backplanes and more than one optical interconnect invention, broadcast systems are typically employed that share the utility of the provided communications path. Broadcast systems create contention for resources as well as interference between communication channels.
Another common problem with backplane and midplane designs is the notion of upgradeability. Backplanes have been historically designed so as not to contain any active components since they represent a single point of failure for the system that employs them. This is true of the present invention which provides interconnects without active components.
The present invention also provides a simple means to upgrade the capacity of a given backplane in the field simply by attaching additional waveguide plates to the backplane which are available to serve new circuit board assemblies added to the system while existing circuit board assemblies continue to perform their functions. This is another important quality of the present invention since it can be used to prevent the need for what is known in the art as a forklift upgrade.
So, there is a need for an alternative to electrical backplanes capable of providing inexpensive scaleable bandwidth, reliable operation, a minimum of electrical connections, dedicated communications paths, reduced electromagnetic emissions and has the ability to be upgraded in the field.
The present invention provides a full mesh optical interconnect in which each circuit board assembly is assigned a dedicated optical transmission path to every other circuit board assembly in a communications system. The only electrical connections necessary for each circuit board assembly are electrical power connections.
The present invention provides a full mesh optical backplane having power transmission conductors and a set of optical transmission guides for accommodating a set of circuit board assemblies forming part of an electronic system. Each circuit board assembly is provided with electrical power through power transmission conductors from a centralized source. The optical transmission guides enable direct transmission of data from each circuit board assembly within a system to any and all other circuit boards within the system.
In a preferred embodiment of the invention, individual plates or discs embody optical transmission guides with an assembly or stack of the discs comprising a backplane. The stack of discs is bound together by means of metallic conductors that also provide a means for power transmission. Circuit board assemblies in a system are connected to the backplane in such manner that each circuit board receives power from metallic conductors, and communicates through dedicated optical transmission guides with every other circuit board assembly in the system. Full mesh is the operating condition in which each circuit board assembly communicates over dedicated paths with every other circuit board assembly in a system.
In specific embodiments a plurality of circuit board assemblies and a plurality of optical transmission guides are required. For the simple case of one circuit board, no transmission guides are required. For two circuit board assemblies, two transmission guides are required: one to transmit from the first assembly to the second assembly, and one to transmit from the second assembly to the first assembly. For simplicity, the number of transmission guides can be divided by two to account for the generalized requirement for bi-directional transmission. Thus for example, in a system comprising eight circuit board assemblies, twenty-eight transmission guide pairs are required and each circuit board assembly would be connected to seven transmission guide pairs so that it could communicate directly with each of its circuit board neighbors.
In a preferred embodiment of the invention, each circuit board assembly in the system has a plurality of optical interfaces arranged along an edge of the circuit board, with each optical interface comprising both a transmitter and a receiver. In addition, each circuit board assembly in the system has a plurality of electrical contacts along the same edge to obtain the required electrical power to perform its function. A plurality of electrical contacts are provided to enhance the reliability of the power distribution means.
The present invention provides a full mesh optical interconnect in several embodiments without expensive optical elements, resorting to unproven or costly manufacturing processes, fundamental changes to the construction of related circuit board assemblies, line of sight optical connections, bonding fiber-optic cables to integrated circuit waveguides, or strictly limiting upgrades to forklift upgrades.
Specific examples are included in the following description for purposes of clarity, but various details can be changed within the scope of the present invention.
An object of the invention is to provide a full mesh optical interconnect for electronic systems enabling high bandwidth dedicated connections between each circuit board assembly and every other circuit board assembly in the system.
Another object of the invention is to provide optical interconnects having optical transmission guides with each guide being in optical isolation from all optical guides in the backplane.
Another object of the invention is to provide optical interconnects having scaleable means for increasing mesh size as the number of circuit boards is increased thereby adding dedicated pairs of optical transmission guides between circuit boards.
Another object of the invention is to improve reliability of electronic systems.
Another object of the invention is to reduce the number of electrical connections required for each circuit board in the system.
Another object of the invention is to reduce electromagnetic emissions of communications systems.
An object of the invention is to provide a full mesh optical backplane enabling dedicated connections between each circuit board assembly and every other circuit board assembly in the system in an economical manner.
Another object of the invention is to provide mating structures for optical waveguides that allow for abutment of an additional set of waveguides for extending an optical path directly to a circuit board assembly.
Another object of the invention is to minimize length of optical paths and thereby minimize transmission delay in optical signals.
Another object of the invention is to provide electrical isolation of the circuit board assemblies in a system.
Another object of the invention is to minimize surface area of optical interconnects such as backplanes thereby to minimize air flow restrictions and improve heat dissipation.
Other and further objects of the invention will become apparent with an understanding of the following detailed description of the invention or upon employment of the invention in practice.